The Development And Study Of Low Ag Sn-0.3Ag-0.7Cu-XBi Lead-free Solder

Due to increasing environment and health concerns over the use of lead, Pb- free electronic manufacture has turned into an implementary stage. Due to reducing the price of existing lead-free solders, and improving their aging performance of high temperature, the development of low Ag lead-free solders play an important part all over the world. A sort of low Ag lead-free solder Sn- 0.3Ag-0.7Cu is developing now, but it has a higher melting point and a worse wettability. Therefore, this thesis aims to study a sort of new low Ag lead-free solder Sn-0.3Ag-0.7Cu-XBi. By contrastive experiments, the influences of Bi on the melting point, wettability and mechanical property of Sn-0.3Ag-0.7Cu lead- free solder alloy are studied and the solder alloy component of favorable combination property are gotten. So that the lead-free solder alloys of lower price, lower melting point, better wettability and excellent combination property are developed.The results of melting point experiment show that the melting point of low Ag lead-free solder Sn-0.3Ag-0.7Cu is 222.6℃. And the melting point of Sn- 0.3Ag-0.7Cu-3.0Bi lead-free solder reduces to 217.3℃, this value conforms to the internationally recommendatory melting point of Sn-Ag-Cu lead-free solders. The results of wettability experiment show that low Ag lead-free solder Sn-0.3Ag-0.7Cu has a worse wettability. And wetting time of Sn-0.3Ag-0.7Cu-3.0Bi lead-free solder at 240℃reduces to 2.337s from 4.597s of the former, reduces at 49.2%, and this value meets the practically mechanisation requirement t≤2.5s. At the same time, this componential lead-free solder has a maximal wetting force Fmax=3.21mN, this value also meets the practically mechanisation requirement Fmax≥3.0mN. Therefore, Sn-0.3Ag-0.7Cu-3.0Bi lead-free solder has a favorable wettability. The results of tensile test show that the tensile strength of low Ag lead-free solder Sn-0.3Ag-0.7Cu is 37.2MPa. And Sn-0.3Ag-0.7Cu-3.0Bi lead-free solder has an obvious increase in tensile strength, namely a maximal tensile strength 77.5MPa, increases at 108.3%.The results of micro-mechanical property in nano-indentation test show that low Ag lead-free Sn-0.3Ag-0.7Cu bulk solder has a higher Young's modulus E 47.152GPa, and the Young's modulus E of Sn-0.3Ag-0.7Cu as-cast BGA solder and as-welded BGA solder respectively reduces to 27.146GPa and 28.436GPa, respectively reduces at 42.4% and 39.7%. And value of stress rate sensitivity n respectively increases from 10.235 to 13.046 and 16.155, respectively increases at 27.5% and 36.6%. Both two parameters E and n take on a typical phenomenon of dimensional effect.